In general, X-ray, MRI, or ultrasound is used in visualization of an inside structure of the human body or the substance. However, the methods can not visualize electrical properties of the human body or the substance.
As an effort for solving the problem, a method for visualizing current density distribution of an inside of a measuring object using the MRI is initially suggested by a research team of the Toronto University in 1989, and, thereafter, there have been active researches related thereto. This is the Current Density Imaging (CDI) technique. In the present CDI, a magnetic flux density B due to an injected current I is measured by using MRI technique, and a current density J is calculated by using the Ampere's law J=1/μ0∇×B, for visualizing an inside current density distribution.
However, the CDI has a drawback in that rotation of the measuring object in an MRI scanner is required for obtaining the magnetic flux density B having three components Bx, By, and Bz. This is because the MRI scanner can only measure a z-directional component, a direction the same with a main magnetic field, of the flux density, i.e., Bz, when the measuring object is in the MRI scanner. That is, since the component the MRI scanner can measure at a time is only the Bz component, for obtaining all the required three components of the magnetic flux density vector, the present CDI technique has a serious drawback of requiring the measuring object (the human body, or the substance) to be rotated in the MRI scanner.
Meanwhile, as a known method for visualizing the electrical properties of the human body, or the substance, there has been Electrical Impedance Tomography (EIT) that has been under active research starting from late 1970s. The EIT provides an image of resistivity (or conductivity) distribution, an electrical property of the measuring object.
In the EIT mostly taking the human body as the measuring object, many electrodes are attached on a surface of the human body, for visualizing the resistivity distribution of an inside of the human body. The visualization of the human body 3according to the resistivity is made possible since tissues of the human body, such as blood, bones, lung, heart, and the like have electrical properties different from one another.
However, due to a fundamental drawback of the EIT, an image of the EIT is poor, to support only a low resolution. That is, EIT has a fundamental drawback in that a current-voltage data measured by EIT is extremely insensitive to variation of resistivity of an inside of the human body. Therefore, clinical application of EIT is not active, presently.